118 
NATURAL SELECTION. 
Chap. IV. 
and the tendency to variability is in itself hereditary, 
consequently they will tend to vary, and generally 
to vary in nearly the same manner as their parents 
varied. Moreover, these two varieties, being only 
slightly modified forms, will tend to inherit those ad¬ 
vantages which made their parent (A) more numerous 
than most of the other inhabitants of the same country; 
they will likewise partake of those more general advan¬ 
tages which made the genus to which the parent-species 
belonged, a large genus in its own country. And these 
circumstances we know to be favourable to the pro¬ 
duction of new varieties. 
If, then, these two varieties be variable, the most 
divergent of their variations will generally be preserved 
during the next thousand generations. And after this 
interval, variety oi} is supposed in the diagram to have 
produced variety which will, owing to the principle 
of divergence, differ more from (A) than did variety 
a^. Variety w} is supposed to have produced two 
varieties, namely and differing from each other, 
and more considerably from their common parent (A). 
We may continue the process by similar steps for any 
length of time ; some of the varieties, after each thousand 
generations, producing only a single variety, but in a 
more and more modified condition, some producing two 
or three varieties, and some failing to produce any. 
Thus the varieties or modified descendants, proceeding 
from the common parent (A), will generally go on in¬ 
creasing in number and diverging in character. In 
the diagram the process is represented up to the ten- 
thousandth generation, and under a condensed and sim¬ 
plified form up to the fourteen-thousandth generation. 
But I must here remark that I do not suppose that 
the process ever goes on so regularly as is represented in 
the diagram, though in itself made somewhat irregular. 
